No matter how high one's tolerance for cold weather, egg nog and three-part harmony, there comes a time in every Christmas caroler's evening when he or she thinks to themselves, Why am I doing this?

Christmas carols today carry cozy connotations of ancient traditions as old as King Wenceslas, but Christmas caroling as we know it dates back to the 19th Century and not much further. In fact, caroling itself didn't always involve Christmas, and the ancient tradition of traveling from house to house to wish neighbors good cheer didn't always involve singing. There's a distinction to be made between carols  songs stemming from medieval musical traditions  and today's Christmas caroling, says Daniel Abraham, musicology expert and choral director at American University in Washington, D.C. "The concept of carol in its origins has actually nothing to do with Christmas," Abraham says. Medieval carols were liturgical songs reserved for processionals in the 12th and 13th centuries. And though modern carols sometimes take their form from these original carols  starting with a refrain, followed by verses of uniform structure  they're separate entities. (See the 10 worst Christmas movies.)

The act of traveling to different homes comes from a different tradition altogether, albeit a similarly ancient one. In England, the word wassail  derived from the Old Norse ves heill meaning "be well, and in good health"  came to mean the wishing of good fortune on your neighbors. No one is quite sure when the custom began, but it did give us the song, "Here We Come-A-Wassailing"  sung as carolers wished good cheer to their neighbors in hopes of getting a gift in return. ("A Wassailing" also evolved into the popular "We Wish You a Merry Christmas"  its last verse, "Bring us some figgy pudding" stems from the wassailers' original intent.)

The two traditions of singing and visiting first merged in Victorian England, as church carols began to merge with Christian folk music. At that time, it was far from a Christmas tradition; festivals like May Day were deemed worthy of caroling, too, but the repertoire as well as early records of this are pretty unclear. In the 19th Century, as Christmas became more commercialized and popular, publishers began churning out anthologies of carols, many which were ancient hymns, also circulating them in broadsheets.

Many of our today's most popular carols date to this period. Christmas Carols Ancient and Modern published in London by British lawyer William B. Sandys in 1833, was the first to print "God Rest Ye Merry Gentlemen," "The First Noel" and "Hark! the Herald Angels Sing." "Joy to the World" first appeared in the Anglican Church hymnal Hymns Ancient and Modern in 1861. Composed by Isaac Watts, known as the "father of Englsh hymnody", the song actually wasn't written exclusively for singing at Christmastime. Charles Wesley's "Hark the Herald Angels Sing" was originally "Hark! How All The Welkin Rings!" (Welkin means sky or heaven, and came to mean making a loud sound.)

Ubiquitous holiday TV ads to the contrary, American caroling is far less common than it used to be, says Bob Thompson, professor of popular culture at Syracuse University. It's not unusual to see carolers standing still in a shopping mall or churchyard, but as for the random groups of friends traipsing to your doorstep for singing, don't count on it. "You talk to most baby boomers they might have a caroling story or two," says Thompson. "Talk to anybody born after 1960 or so and it's become much less common." Simply put, times and culture have changed. "The singing of Christmas carols at a stranger's door assumes a similarity of culture among carolers and audience," says Chris Brunelle, an assistant professor of classics at St. Olaf college. With America a far more diverse and less homogenous society than it was in caroling's heyday, that's a larger assumption than many are comfortable with. Still, most of us probably agree about the egg nog.